Density functional theory strategies

Density functional theory-based methods ultimately derive from quantum mechanics research from the 1920 s, especially the Thomas-Fermi-Dirac model, and from Slater s fundamental work in quantum chemistry in the 1950 s. The DFT approach is based upon a strategy of modeling electron correlation via general functionals of the electron density. 

The electronic coupling of donor and acceptor sites, connected via a t-stack, can either be treated by carrying out a calculation on the complete system or by employing a divide-and-conquer (DC) strategy. With the Hartree-Fock (HF) method or a method based on density functional theory (DFT), full treatment of a d-a system is feasible for relatively small systems. Whereas such calculations can be performed for models consisting of up to about ten WCPs, they are essentially inaccessible even for dimers when one attempts to combine them with MD simulations. Semiempirical quantum chemical methods require considerably less effort than HF or DFT methods also, one can afford application to larger models. However, standard semiempirical methods, e.g., AMI or PM3, considerably underestimate the electronic couplings between r-stacked donor and acceptor sites and, therefore, a special parameterization has to be invoked (see below). 

We will of course be rather more focused here. We shall be concerned with the generic computational strategies needed to address the problems of phase behavior. The physical context we shall explore will not extend beyond the structural organization of the elementary phases (liquid, vapor, crystalline) of matter, although the strategies are much more widely applicable than this. We shall have nothing to say about a wide spectrum of techniques (density functional theory [1], integral equation theories [2], anharmonic perturbation... 

Os). There also exist a number of volatile Ru and Os halides and oxyhalides. The fluorides and oxyfluorides are of importance, but experimentally difficult to handle. Quite naturally, early considerations [81,82] and experimental developments [83-96] for a first Hs chemistry exclusively concentrated on the tetroxides. This strategy is justified, since classical extrapolations [97] as well as fully relativistic density functional theory calculations on the group-8 tetroxides [98] predict the existence of a volatile and very stable HSO4. 

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